1. Technical Field
The present disclosure relates to a method and device for detecting anomalous events for an electronic apparatus, in particular a portable apparatus, for example for detecting free-fall events, to which the ensuing treatment will make particular reference, without this implying any loss of generality.
2. Description of the Related Art
As is known, portable electronic apparatuses can easily be subjected during their normal use to potentially harmful or even destructive events, such as free-fall events, impact, high vibrations, or shock in general. These events are herein defined as “anomalous events”, in so far as they are extraneous to a condition of normal use or operation of portable apparatuses (a so-called “normal mode” condition). In particular, the normal-mode condition is defined by the set of actions (for example, actuation of keys or pushbuttons, displacements, rotations, etc.) and by the external conditions (for example, environmental conditions) normally associated with the use of the portable apparatus.
Anomalous events are particularly harmful in the case where the portable apparatuses are provided with a hard-disk unit. In fact, in a hard disk, a read/write head is generally kept at a minimum distance of separation from a storage medium (a magnetic film carried by a rotating disk). In the case of a fall or other shock, the read/write head can collide with the storage medium and thus cause damage to the hard disk and/or irreversible loss of stored data.
In order to prevent, or at least limit, occurrence of destructive events, it has been proposed to use detection devices within the portable apparatuses, designed to detect occurrence of a particular anomalous event (for example, a fall or a shock) and to implement suitable actions of protection. For example, once the anomalous event has been detected, it is possible to issue a command for forced “parking” of the read/write head of a hard disk of the portable apparatus, which is brought into a safe area (for example, the position assumed by the head with the apparatus turned off).
Detection devices generally operate on the basis of detection of accelerations acting on the portable apparatuses, and are provided, for this purpose, with accelerometric sensors, in particular microelectromechanical (MEMS) inertial sensors made using the semiconductor technologies, which prove advantageous given their small size.
As is known, an inertial sensor of a microelectromechanical type in general comprises a mobile mass, suspended above a substrate, and anchored to the substrate and to a corresponding package via elastic elements. Mobile electrodes are fixedly coupled to the mobile mass, and fixed electrodes, capacitively coupled to the mobile electrodes, are fixedly coupled to the substrate. In the presence of an acceleration, the mobile mass undergoes a displacement with respect to the substrate, which brings about a capacitive variation of the capacitor formed between the mobile electrodes and the fixed electrodes. Starting from the capacitive variation, via appropriate processing operations, it is possible to determine the value of the acceleration acting on the sensor. In particular, also in conditions of rest, the inertial sensor detects a non-zero acceleration, due to the effect of the Earth's gravitational acceleration (g), which determines in any case a displacement of the mobile mass with respect to a position of equilibrium.
Detection of anomalous events by the protection devices is generally based on the result of the comparison between an instantaneous absolute value of acceleration, measured by the corresponding inertial sensors, and one or more acceleration thresholds.
For example, in the case of the free-fall event, the portable apparatus, and the inertial sensor fixed thereto, are to a first approximation subject only to the Earth's gravitational acceleration (g). In this condition, both the mobile mass and the package of the inertial sensor are subjected to the same acceleration (g) so that the displacement of the mobile mass with respect to a reference system fixed with respect to the package, also in free-fall conditions, is zero, as also is the acceleration detected. Consequently, a free-fall condition is detected when the resultant acceleration detected is lower than a pre-set threshold, or, alternatively, when the values of the individual components of acceleration detected along a first axis, a second axis, and a third axis of a set of three Cartesian axes fixed with respect to the inertial sensor drop simultaneously below the pre-set threshold. In its simplest embodiment, the algorithm for free-fall detection hence requires only definition of a threshold value and comparison of the instantaneous values of acceleration with this threshold. Usually, a control is added on the time length of the free-fall event detection so as to reject false detections that have a duration shorter than a given time interval (for example, 90 ms).
A shock acting on the portable apparatus is detected in a substantially similar way by verifying that a given threshold has been exceeded by the instantaneous acceleration acting on the portable apparatus.